Microwave phase shift device



i a M@ Z I: 35 Z/ 4/ v g- 1970 o. c. STAFFORD ET AL 3,522,558

MICROWAVE PHASE SHIFT DEVICE Filed Jan. 13, 1969 "HM 1 25 I 36 Q i tl T r 7 2 E a4 Tag 5 4f A5 JFSE W21 5 5 JNVE'NTUES Q C7. C. ST'HFF'UE'D 5 .1.0. VDE'LC'KEF? United States Patent Office 3,522,558 Patented Aug. 4, 1970 York Filed Jan. 13, 1969, Ser. No. 790,562 Int. Cl. H03h 7/30; H01p 1/18 U.S. Cl. 333-31 6 Claims ABSTRACT OF THE DISCLOSURE A microwave phase shifter wherein a carriage is movably mounted within an outer housing which has input and output connectors fixed to opposite walls thereof. A first flexible, conductive tape extends from the input connector around a series of guide rollers and onto a takeup spool mounted on the carriage. Similarly, a second flexible, conductive tape extends from the output connector around a second series of guide rollers and onto a second takeup spool. Two of the guide rollers are spring biased toward one another so that the two tapes are held into contact with one another to form a complete transmission line between the input and output connectors. Movement of the carriage in one direction within the housing unrolls portions of the tapes from their respective takeup spools and increase the effective lengths of the transmission line and hence change the phase shift between the input and output connectors. Movement of the carriage in the opposite direction provides the opposite effect. Additionally, a pair of resilient contact clips are provided to ground the trailing ends of the tapes one quarter wavelength from the contact point between the tapes to isolate the trailing tapes from the line.

GOVERNMENT CONTRACT The invention herein claimed was made in the course of, or under contract with the United States Army.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to a mechanical device for shifting the phase of a microwave signal. In certain circuit applications, it is necessary to provide a precise amount of phase shift between an input and an output terminal; for example, in the balancing of a phase-sensitive bridge or in phasing a plurality of microwave antennas. Concurrently, the phase shifter should not introduce losses or attenuation into the circuit.

Description of the prior art In the past, a number of different mechanical phase shifting devices have been devised, most of which employ a movable contact which may be physically displaced along a section of transmission line connected between an input and an output terminal. The movable contact enables signals of varying phases to be extracted from different points of varying displacement along the line. However, most of these prior art adjustable transmission lines have proven unsatisfactory in that the movable contact invariably becomes noisy and erratic in operation after a period of use.

SUMMARY OF THE INVENTION In one embodiment of the invention, a microwave phase shifter is contemplated wherein a pair of flexible conductors extend from input and output terminals, respectively, to separate takeup spools. The two conductors are in adjustable conductive engagement so that the length of the transmission path formed between the terminals may be varied to shift the phase of microwave signal from input to output. More particularly, means are also provided for grounding the conductors at a distance of one quarter wavelength, at the frequency of operation, from the point of conductive engagement to isolate the trailing ends of the conductors from the transmission path.

BRIEF DESCRIPTION OF THE DRAWING The nature of the present invention and its various advantages will appear more fully by referring to the following detailed description in conjunction with the appended drawing, in which:

FIG. 1 is a top view of a mechanical phase shifter constructed in accordance with the invention;

FIG. 2 is a sectional view taken along the lines 22 of FIG. 1; and

FIGS. 30 and 3b are schematic representations of the electrical characteristics of the phase shifter shown in FIG. 1.

DETAILED DESCRIPTION Referring to FIG. 1, the phase shifter includes a metal outer housing 11 having an input coaxial connector 12 and an output coaxial connector 13 mounted on opposite sides thereof. The connectors 12 and 13 are of the standard coaxial, bayonet type and have their outer conductors electrically joined to the housing 11. When input and output coaxial transmission lines are coupled, respectively, to the connectors 12 and 13, the outer conductors of the transmission lines are electrically joined through the metal housing 11. The housing and outer conductors of the transmission lines are usually electrically grounded.

The opposed inner walls of the housing 11 carry a pair of inwardly projecting tongue portions 14 and 15 extending the length of the walls. A movable metal carriage 16 is slidably mounted within the housing 11 by a pair of grooves along its edge (not shown) which mate with the tongues 14 and 15. A threaded shaft 17 is rotatably attached to the carriage 16 at one end by a joint 18 and extends through and threadably engages one wall of the housing 11. The threads of the shaft engage threads in the housing so that rotation of the shaft 17 by means of a handle 19 reciprocates the carriage 16 along the tongue guideways 14 and 15 of the housing 11.

The movable carriage 16 has rotatably mounted, within recessed portions thereof, two sets of primary tape guide rollers 21, 22, and 23, 24. The carriage also rotatably mounts two pairs of secondary tape guide rollers 25, 26 and 27, 28, two bottom rollers 36 and 38 and two tape takeup spools 31 and 32. Each of the rollers is preferably made of an insulative material such as nylon" or Teflon.

The inner conductor of the input connector 12 is connected to one end of a first flexible conductor which may comprise a conductive solid metal tape 33. However, because of the difliculty in finding a solid metal tape which is both strong and ver flexible, the tape preferably comprises a strip of flexible insulative material such as polyethyleneterephthalate, sold under the trade name Mylar, both surfaces of which are covered with a conductive layer of metal foil. The conductive layer is electrically continuous on both sides of the tape. The tape 33 is passed from the inner conductor of the connector 12 through a block of insulating material 35, around the two primary guide rollers 21 and 22, over the bottom roller 36, around the two secondary guide rollers 26 and 25 and is fastened to the takeup spool 31. The takeup spool 31 is spring biased (by means not shown) to maintain a constant, uniform tension on the tape 33 and hold it in engagement with the guide rollers regardless of the position of the carriage 16 within the housing 111. Similarly, a second tape 34, identical in construction to the first tape 33, is connected from the inner conductor of the output connector 13 through an insulator 37 around the primary guide rollers 24 and 23, the bottom roller 38, over the secondary guide rollers 27 and 28 and around the takeup spool 32 to which it is fastened. The takeup spool 32 is also spring biased to maintain a constant tension on the second tape 34.

The two innermost primary guide rollers 22 and 23 are additionally spring biased toward one another so that the adjacent conductive surfaces of the two tapes 33 and 34 are held in constant electrical contact with one another. A pair of resilient, metal grounding clips 41 and 42 are constructed to be removably inserted into selected ones of a plurality of receiving grooves 43, 44 which are formed in the recessed channel in the carriage 16 through which the tapes 33 and 34 extend. The clips 41 and 42 are resiliently biased toward one another to press the adjacent conductive surfaces of the tapes 33 and 34 into engagement with one another and electrically connect the tapes at that point to ground through the metal body of the housing 11. The exact function of these clips will be explained below.

FIG. 2 shows a sectional view looking along the sectional line 22 of FIG. 1, and shows how the conductive tape 34 is passed over the primary guide roller 23 across the conductive clip 42 and around the guide roller 38.

In operation, the effective electrical length of the transmission line connected between the input connector 12 and the output connector 13 is the length of the tape 33 from the inner conductor of the input connector 12 to the point of electrical contact between the tape 33 and the tape 34 (between primary guide rollers 22 and 23) plus the length of the tape 34 from the contact point to the inner conductor of the output connector 13. By rotating the handle 19 and turning the threaded shaft 17, the carriage 16 is reciprocated within the housing 11. Movement of the carriage 16 in a direction away from the handle 19 lengthens the total effective electrical length of the transmission line connected between the input connector 12 and the output connector 13 because as the carriage moves, the tapes 33 and 34 are unrolled from the takeup spools 31 and 32, respectively. Likewise, movement of the carriage 16 toward the handle 18 decreases the effective electrical length of the transmission line because the tapes withdraw onto their respective takeup spools. Variations in line length, of course, serves to shift the phase of the signal between the input and output terminals.

At first glance, a problem is presented by all of the excessive conductive tape extending from between the point of contact between rollers 22 and 23 onto the takeup spools 31 and 32. Due to the capacitive coupling between the tapes and the grounded metal framework of the carriage 16 as well as the inductive effect of the coiled tapes on the takeup spools, an electrical load 45 is placed upon the transmission line as illustrated in FIG. 3a. This load is effectively isolated from the remainder of the transmission line by positioning the resilient metal clips 41 and 42 within the slots 43 and 44 so that the distance between the contact point of the tapes 33 and 34 between the clips and the contact point between the rollers 22 and 23 is exactly one quarter of a wavelength at the frequency of operation. As is well known in the art, a shorted or grounded stub which is a quarter wavelength long is electrically an open circuit and does not provide either a loading impedance or a phase shift in the circuit to which it is coupled. Practically, the position of the clips 41 and 42 may sometimes vary slightly from a quarter of a wavelength from the contact point depending upon other factors of the phase shifter.

The electrical characteristics of the phase shifter shown in FIG. 1, is illustrated in FIGS. 3a and 3b. FIG. 3a shows how the phase shifter is basically two series connected variable length transmission lines, which are ganged together in operation, connected between the input connector 12 and the output connector 13. The parallel LC circuit 45, connected between the junction of the two transmission lines and ground illustrates the loading effect which the excess conductive tapes would have upon the variable transmission lines. FIG. 3b illustrates how the transmission lines are isolated from a ground by an open circuit when the grounding clips 41 and 42 are positioned so that the parallel circuit to ground connected to the transmission line is one quarter wavelength. The clips 41 and 42 may be moved to various ones of the slots 43 and 44 in order to make the distance thereto from the point of contact of the tapes 33 and 34 between rollers 22 and 23 approximately one quarter wavelength. This distance will vary, of course, depending upon the frequency of operatlon.

It is to be understood that the above-described embodiments are simply illustrative of the invention and that many other embodiments can be devised without departing from the scope and spirit of the invention.

What is claimed is:

1. A microwave phase shifter comprising:

an input terminal;

an output terminal;

a first flexible conductor having one end connected to said input terminal and the other connected to a first takeup spool;

a second flexible conductor having one end connected to said output terminal and the other connected to a second takeup spool, said second conductor being in physical, conductive engagement with said first conductor at a point between the respective terminals and takeup spools to form a conductive signal transmission path between said terminals; and

means for varying the point of engagement of said first and second conductors to vary the length of the conductive signal transmission path between said input terminal and said output terminal and shift the phase of microwave signals placed upon said input terminal.

2. A microwave phase shifter as set forth in claim 1, also including:

first and second non-conductive guide rollers rotatably mounted contiguous to one another and spring biased toward one another to bring their respective surfaces into contact; and

wherein said first and second conductors extend from their respective terminals, over said first and second guide rollers, respectively, to their respective takeup spools, said spring biased rollers urging said first and second conductors into physical, conductive engagement to form the conductive signal transmission path between said terminals.

3. A microwave phase shifter as set forth in claim 1, also including: means for grounding both of said conductors between their point of engagement and said takeup spools, said ground point being spaced from said point of engagement a distance of one quarter wavelength at the selected frequency of operation to isolate the remainder of said conductors from said signal transmission path.

4. A device for shifting the phase of a microwave signal between an input coaxial terminal and an output coaxial terminal, comprising:

a metal housing mounting said input and output coaxial terminals, the outer conductors of said coaxial terminals being in electrical contact with the body of said housing;

a metal carriage movably mounted within said housing;

a pair of non-conductive guide rollers rotatably mounted on said carriage, one roller of said pair being spring biased toward the other to bring their respective surfaces into contact;

first and second takeup spools rotatably mounted on said carriage, said spools being spring biased in one rotation direction to maintain a tension thereon;

a first flexible conductor extending from the inner conductor of the input coaxial terminal over a first roller of said pair of rollers and having the trailing end thereof Wound upon said first takeup spool in a direction to maintain tension upon said conductor;

a second flexible conductor extending from the inner conductor of the output coaxial terminal over the second roller of said pair of rollers and having the trailing end thereof wound upon said second takeup spool in a direction to maintain tension upon said conductor, said spring biased rollers urging said first and second conductors into physical engagement to form a conductive signal transmission path between said input and output terminals; and

means for reciprocating said carriage within said housing to vary the point of physical engagement between said first and second conductors and thereby vary the length of the conductive signal transmission path between said input and output terminals to shift the phase of a microwave signal between said input and output terminals.

5. A device for shifting the phase of a microwave signal as set forth in claim 4 which also includes: means con- References Cited UNITED STATES PATENTS 7/1946 Pickles 3333l 10/1968 Wendolkowski 3333l X HERMAN KARL SAALBACH, Primary Examiner M. NUSSBAUM, Assistant Examiner US. Cl. X.R. 33384, 97 

